In a reciprocating piston internal combustion engine, a connecting rod transmits forces between a piston and a crankshaft. The piston and, in many cases, the connecting rod have bushings which receive a piston pin to secure the piston to the connecting rod. Since the connecting rod rocks with respect to the piston, oil is supplied to lubricate the interengaging surfaces of the pin and the bushings.
Adequate lubrication of these surfaces is more difficult in a two-stroke cycle engine than in a four-stroke cycle engine. In a four-stroke cycle engine, oil flows between the surfaces during the intake stroke when the load of the bushings on the pin reverses. In a two-stroke cycle engine, on the other hand, the bushings are continuously loaded against the pin and oil flow between the surfaces is hindered.